Fix the length recycling issue with Quarto.

[olivroy]

Summary

Fixes #1985 .

In brief, this

  text[nzchar(text, keepNA = FALSE)] <- non_na_text

didn't return text correctly. It returned non_na_text, (can be of shorter length if ““ is present, hence the warning + bad output:

Warning:
In body[[col]][rows][!is.na(result)] <- omit_na(result) :
  le nombre d'objets à remplacer n'est pas multiple de la taille du remplacement
Calls: <Anonymous> ... <Anonymous> -> render_as_html -> build_data -> render_formats

---
date: "`r Sys.Date()`"
---

```{r}
#| echo: false
#| warning: false
#| message: false

library(gt)
```

```{r}
#| echo: true

# "" (no space) in comment treated as non-existent, so vector is (erroneously) recycled
data <- mtcars[1:5, ]
data$comment <- c("test", "`test`", "", "test", "")
data |> 
  gt()|>
  fmt_markdown(columns = comment)
```

edit: I misread. this fixes #1985
bug introduced in #1855

[rich-iannone]

LGTM, thanks!!